Double-resonator micro-speaker assemblies and methods for tuning the same

ABSTRACT

Micro-speaker assemblies and mobile terminals including micro-speaker assemblies are provided. The micro-speaker assemblies include a micro-speaker positioned in a housing. A first forward tuning volume is positioned adjacent a front face of the micro-speaker. A passageway extends from the first forward tuning volume to an opening in the housing. A second forward tuning volume in fluid communication with the passageway is positioned at a location between the first forward tuning volume and the opening in the housing. The second forward tuning volume, the first forward tuning volume and the passageway define a double-resonator that tunes a frequency response of the micro-speaker. Methods for tuning micro-speakers are also provided.

RELATED APPLICATION

This application claims priority to and is a continuation of parentapplication Ser. No. 10/256,745, filed Sep. 27, 2002, now U.S. Pat. No.7,123,736 the disclosure of which is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to speaker assemblies for personal usesuch as in cellular telephones and, more particularly, to tunedmicro-speaker assemblies.

Manufacturers and designers of personal electronic devices, such ascellular radio telephones, frequently seek to reduce the overalldimensions of such devices while maintaining attractive stylecharacteristics for the devices. One consequence of the reduced size forsuch devices that include a speaker is that less space may be availablefor the speaker. Furthermore, a variety of audio signal generationcapabilities may be desired in such personal electronic devicesincluding buzzers, voice signal generation and/or music or other higherfrequency band signal reproduction and playback.

As the space available for the hardware supporting the audio signalgeneration capabilities decreases in the personal electronic devices, itmay become more difficult to support multiple sound emitting outputdevices and the space available for each such device may become smaller.Furthermore, increased functionality in such personal electronic devicesmay require more of the reduced available space to be utilized for otherfunctionality of the device. The reduction in the size of the audiooutput devices may also increase the difficulty of providing a desirableloudness level for signals, such as buzzer alert signals. In addition,to the extent features of the audio output device(s) are presentedexternally on the personal electronic device, the impact of thosefeatures on the appearance of the product and the flexibility to placesuch visible features at different locations on the device may becomeimportant.

For audio performance, it is known to use a speaker having relativelyuniform frequency characteristics in the 300 hertz (Hz) to 3400 Hz voicefrequency band. Where music or other complex signals are provided by thedevice, a speaker with a frequency range providing a bandwidth up to atleast about 8000 Hz may be used. In addition, louder alert signals maybe provided in various personal electronic devices.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide micro-speaker assembliesand mobile terminals including micro-speaker assemblies. Themicro-speaker assemblies include a micro-speaker positioned in ahousing. A first forward tuning volume is positioned adjacent a frontface of the micro-speaker. A passageway extends from the first forwardtuning volume to an opening in the housing. A second forward tuningvolume in fluid communication with the passageway is positioned at alocation between the first forward tuning volume and the opening in thehousing. The second forward tuning volume, the first forward tuningvolume and the passageway define a double-resonator that tunes afrequency response of the micro-speaker.

In other embodiments of the present invention, micro-speaker assembliesare provided including a micro-speaker positioned in a housing. Adouble-resonator acoustically coupled to the micro-speaker has a firstresonance frequency at an alert frequency above the voice frequency bandand a second resonance frequency above the first resonance frequency.The first resonance frequency may be between about 3400 hertz (Hz) and5000 Hz and the second resonance frequency may be between about 4000 Hzand about 10000 Hz. In particular embodiments of the present invention,the first resonance frequency is between about 3000 hertz (Hz) and about4000 Hz and the second resonance frequency is between about 6000 Hz andabout 8000 Hz.

In further embodiments of the present invention, methods are providedfor tuning a micro-speaker. A volume of a first forward tuning volumeadjacent a front face of a micro-speaker is selected to define a firstresonant frequency of the micro-speaker. The first resonant frequencyprovides an amplitude response in a voice frequency range and a highamplitude response, greater that the response in the voice frequencyrange, at the first resonant frequency. A volume of a second forwardtuning volume and a position of the second forward tuning volume on apassageway of the micro-speaker assembly extending from the firstforward tuning volume to an opening in a housing containing themicro-speaker assembly are selected to define a second resonantfrequency of the micro-speaker. The second resonant frequency is greaterthan the first resonant frequency. The second resonant frequencyprovides an amplitude response up to at least about 8000 hertz (Hz).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a mobile terminalincluding a tuned micro-speaker assembly according to embodiments of thepresent invention;

FIG. 2 is a schematic cross-section illustrating a tuned micro-speakerassembly according to embodiments of the present invention;

FIG. 3 is a schematic diagram illustrating a mechanical to acousticalanalogy model of the tuned micro-speaker of FIG. 2;

FIG. 4 is a semi-logarithmic graph illustrating predicted frequencyresponse through an extended frequency range for tuned micro-speakerassemblies according to embodiments of the present invention withdifferent second tuning volume configurations;

FIG. 5 is a semi-logarithmic graph illustrating frequency responsethrough an extended frequency range for tuned micro-speaker assembliesaccording to embodiments of the present invention with different secondtuning volume configurations;

FIG. 6 is a semi-logarithmic graph illustrating frequency responsethrough an extended frequency range for a tuned micro-speaker assemblyaccording to embodiments of the present invention; and

FIG. 7 is a flow chart illustrating operations for tuning amicro-speaker assembly according to embodiments of the presentinvention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. In the drawings, the relativesizes of regions or features may be exaggerated for clarity. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art.

The present invention is described below with reference to flowchartillustrations and/or block and/or flow diagrams of methods and mobileterminals or micro-speaker assemblies according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations related to methods, and combinations of blocks in theflowchart illustrations, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions specified in the flowchart and/or blockand/or flow diagram block or blocks.

Embodiments of the present invention will now be described withreference to the schematic block diagram illustration of a wirelessterminal in FIG. 1. FIG. 1 illustrates an exemplary radiotelephonecommunication system, in accordance with embodiments of the presentinvention, which includes mobile wireless terminal 22 and a base stationtransceiver 24 of a wireless communications network. The mobile terminal22 includes a portable housing 23 and may include a keyboard/keypad 26,a display 28, a micro-speaker assembly 32, a microphone 34, atransceiver 36, and a memory 38 that communicate with acontroller/processor 42. The transceiver 36 typically comprises atransmitter circuit 44 and a receiver circuit 46, which respectivelytransmit outgoing radio frequency signals to the base stationtransceiver 24 and receive incoming radio frequency signals, such asvoice signals, from the base station transceiver 24 via an antenna 48.The radio frequency signals transmitted between the mobile terminal 22and the base station transceiver 24 may comprise both traffic andcontrol signals (e.g., paging signals/messages for incoming calls),which are used to establish and maintain communication with anotherparty or destination. The controller/processor 42 may support variousfunctions of the mobile terminal 22, including decoding received voicesignals from the receiver circuit 42 and providing the decoded voicesignals to the micro-speaker assembly 32. As shown in FIG. 1, musicalinstrument digital interface (MIDI) signals may be supplied to themicro-speaker 32 by a MIDI synthesizer 35 for alerting and/or MMIfeedback. Alternatively, synthesizers for other formats may be provided.

The foregoing components of the mobile terminal 22, other than themicro-speaker assembly 32, may be included in many conventional mobileterminals and their functionality is generally known to those skilled inthe art. It should be further understood, that, as used herein, the term“mobile terminal” may include a cellular radiotelephone with or withouta multi-line display; a Personal Communications System (PCS) terminalthat may combine a cellular radiotelephone with data processing,facsimile and data communications capabilities; a Personal DataAssistant (PDA) that can include a radiotelephone, pager,Internet/intranet access, Web browser, organizer, calendar and/or aglobal positioning system (GPS) receiver; and a conventional laptopand/or palmtop portable computer, that may include a radiotelephonetransceiver, or other portable device using a micro-speaker in a spaceconstrained housing configuration.

In some embodiments of the present invention, the base stationtransceiver 24 comprises the radio transceiver(s) that define anindividual cell in a cellular network and communicate with the mobileterminal 22 and other mobile terminals in the cell using a radio-linkprotocol. Although only a single base station transceiver 24 is shown,it will be understood that many base station transceivers may beconnected through, for example, a mobile switching center and otherdevices to define a wireless communications network.

Although the present invention may be embodied in communication devicesor systems, such as the mobile terminal 22 and/or the base stationtransceiver 24, the present invention is not limited to such devicesand/or systems. Instead, the present invention may be embodied in anyapparatus that utilizes a tuned micro-speaker.

A tuned micro-speaker assembly according to embodiments of the presentinvention will now be further described with reference to the schematicblock diagram illustration of FIG. 2. As shown in the embodiments ofFIG. 2, the micro-speaker assembly 132 includes a micro-speaker 155positioned in a housing 150. Only a portion of the housing 150 is shownin FIG. 2 and the housing 150 may include other components that are notdirectly related to the micro-speaker assembly 132. The micro-speaker155 includes a first face 157 and a second face 159 positioned oppositefrom the first face 157. A first forward tuning volume 160 is locatedadjacent the first face 157 of the micro-speaker 155. A passageway 165extends from the first forward tuning volume 160 to an opening 170 inthe housing 150.

A second forward tuning volume 175 is located in fluid communicationwith the passageway 165. The second forward tuning volume 175 ispositioned at a location between the first forward tuning volume 160 andthe opening 170 in the housing 150. Thus, on the forward side of themicro-speaker 155, the second forward tuning volume 175, the firstforward tuning volume 160 and the passageway 165 define adouble-resonator that tunes the frequency response of the micro-speaker155. As will be further described herein, the double-resonatoracoustically coupled to the micro-speaker 155 may have a first resonancefrequency at an alert frequency above the voice frequency band and asecond resonance frequency above the first resonance frequency. Thefirst resonance frequency may be between about 3400 hertz (Hz) and 5000Hz and the second resonance frequency may be between about 4000 Hz andabout 10000 Hz. In particular embodiments of the present invention, thefirst resonance frequency is between about 3000 hertz (Hz) and about4000 Hz and the second resonance frequency is between about 6000 Hz andabout 8000 Hz. As used herein, “double-resonator” also includes higherorder resonators and the present invention is not limited to resonatorcircuits having only two resonance frequencies.

The micro-speaker assembly 132 may be used as the micro-speaker assembly32 in a mobile terminal 22 such as illustrated in FIG. 1. In such acase, the portable housing 23 of the mobile terminal 22 may serve as thehousing 150 of the micro-speaker assembly 132. It is to be furtherunderstood that, while the illustration of FIG. 2 shows a side opening170 for a micro-speaker assembly 132, the invention is not limited tosuch a porting and may also be ported to the top of the mobile terminal22 or other location, for example, to avoid peak acoustic exposure tohigh sound levels at an earpiece position of the mobile terminal 22without having an unacceptable impact on the frequency response of themicro-speaker 155. In further embodiments, it will be understood thatthe micro-speaker 155 may be ported through or integrated into anantenna or other hardware of the mobile terminal 22, as well as theconfiguration illustrated in FIG. 2, without significant degradation ofthe audio performance of the micro-speaker assemble 132.

As further illustrated in FIG. 2, the micro-speaker assembly 132 mayinclude a back tuning volume 180, which may be located adjacent thesecond face 159 of the micro-speaker 155. While the relative volumes ofthe respective tuning volumes 160, 175, 180 are merely illustrative andnot intended to limit the present invention, in various embodiments ofthe present invention, the back tuning volume 180 is at least an orderof magnitude larger than each of the first forward tuning volume 160 andthe second forward tuning volume 175. For example, the passageway 165may extend about 5 millimeters (mm) and the first 160 and second 175forward tuning volumes may each be less than about 0.2 cubiccentimeters.

Micro-speaker 155, in various embodiments has a diameter of betweenabout 10 millimeters (mm) and about 20 mm. In other embodiments, theopening 170 may have an area of less than about 10 square millimeters(mm²). Such a small port size may be about half the size, or less, oftypical existing porting strategies for micro-speakers. The use of suchsmaller porting size openings for the opening 170 may, for example, bedesirable to reduce interference or detraction from the appearance ofthe mobile terminal 22 or other device in which the micro-speakerassembly 132 is located.

FIG. 3 is a schematic diagram illustrating a mechanical to acousticalanalogy model for the tuned micro-speaker assembly illustrated in FIG.2. In FIG. 3, volumes of the tuning volumes are represented ascompliance FV for the first forward tuning volume 160, TV for the secondforward tuning volume 175, and BV for the back tuning volume 180.Furthermore, the passageway 165 includes a first section 165′ extendingfrom the first forward tuning volume 160 to the second forward tuningvolume 175 and a second section 165″ extending from the second forwardtuning volume 175 to the opening 170 in the housing 150. The signal fromthe speaker 155 radiates from the opening 170 into the air to bereceived by a user or a microphone or other hearing device. As shown inFIG. 3, each of the passageway segments 165′, 165″ is characterized by alength (l) and a diameter (d).

Also shown in FIG. 3 is a frequency generator 185. The frequencygenerator 185, or other signal source, provides a voltage (and/orcurrent) driving signal to the micro-speaker 155.

As seen in FIG. 3, the effect of having two front tuning volumes 160,175 and the passageway 165′, 165″, provides a double-resonator for themicro-speaker assembly 132 which, as will be described further herein,in some embodiments may be used to provide both good alertingperformance and extend the frequency response of the micro-speakerassembly 132 above the voice frequency range.

FIGS. 4-6 are semi-logarithmic graphic illustrations of frequencyresponse for tuned micro-speaker assemblies according to variousembodiments of the present invention. More particularly, FIGS. 4 and 5illustrate the effect of increasing or decreasing the size of the secondforward tuning volume 175 on the frequency response of the micro-speaker155. FIG. 4 illustrates the predicted response of the micro-speaker 155based on a mathematical model of the micro-speaker assembly 132 asillustrated in FIG. 3. The arrow shown in FIG. 4 in the extendedfrequency range above the first resonant frequency shows the trends ofthe curve in the extended frequency range with increasing volume of thesecond forward tuning volume 175. Thus, increased volume of the secondforward tuning volume 175 can be seen to lower the amplitude of thesecond (or higher) frequency resonance point while increasing theamplitude in the extended frequency range above approximately 4000 hertz(Hz). More particularly, the amplitude output illustrated in the graphof FIG. 4 corresponds to a level measured in decibels sound pressurelevel root mean square (referenced to 20 microPascals) (dBSPL_(rms)) at1 centimeter (cm) from the opening 170 of the micro-speaker assembly 132when the frequency generator 185 sweeps through the frequency bandproviding a 1 volt_(rms) input to the micro-speaker 155. Themicro-speaker utilized to generate the results shown in FIG. 4 is an 8ohm, 15 millimeter diameter micro-speaker.

FIG. 5 is a semi-logarithmic graph illustrating test data ofmeasurements from micro-speaker assembly 132 in accordance with themechanical model illustrated in FIG. 3 used to demonstrate the effect ofmicro-speaker tuning in accordance with various embodiments of thepresent invention. For the embodiments illustrated in FIG. 5, the backtuning volume 180 is 2.5 cubic centimeters, the first forward tuningvolume 160 is 0.18 cubic centimeters and the second forward tuningvolume 175 is 0.15 cubic centimeters. The opening 170 is 2.65 millimetersquare (or equivalently, a 3 millimeter diameter providing substantiallythe same opening area where the passageway is a tube). For the resultsillustrated in FIG. 5, the second forward tuning volume 175 ispositioned adjacent a wall 152 defining the housing 150 resulting in asecond passageway section 165″ having a length of 1.5 millimeters,corresponding to the thickness of a typical plastic mobile terminalwall. The first passageway section 165′ has a length of 3.5 millimeters.Again, performance for different volumes of the second forward tuningvolume 175 (up through 0.3 cubic centimeters) are shown by the variouscurves in FIG. 5. In particular, the illustrated response curvescorrespond to a second forward tuning volume of 100 cubic millimeters(mm³) 500, 150 mm³ 505, 50 mm³ 510, 0 mm³ 515, 200 mm³ 520, 250 mm³ 525and 300 mm³ 530.

The performance of a particular selected design of a micro-speakerassembly in accordance with the present invention is further illustratedin the semi-logarithmic graph of FIG. 6. As shown in FIG. 6, secondresonance frequency for the dual-resonator is between 6000 hertz and7000 hertz. The first resonance falls at an alert frequency at or justbelow 4000 hertz. The amplitude lift provided by the second resonancesubstantially nearly doubles the bandwidth of the micro-speaker assemblyabove the voice frequency range of about 300 hertz to about 3400 hertz,providing a bandwidth to the system of about 10,000 hertz. Such anextend frequency response may support, for example, polyphonic ring toneand melodies (such as from a MIDI synthesizer or MP3 file playback orthe like). The placement of the first resonance at about 4000 hertz isselected to provide a high amplitude alerting performance from about3000 hertz to about 4000 hertz (and up to even about 8000 hertz forharmonics of the alerting ring frequency). While the scale has beenchanged for the amplitude displayed in FIG. 6 as compared to FIGS. 3-5,as illustrated in FIG. 6, a one V_(rms) input to the micro-speakeryields a 115 dBSPL_(rms) at resonance, a performance comparable withtypical high quality buzzers in portable devices.

With the performance for the system as illustrated in FIG. 6, inprocessing voice signals, such as in a speaker phone mode for a mobileterminal, as the first resonance is at about 4000 hertz instead of 3000hertz, the effect of a low pass filter, such as may typically be foundin the coder/decoder (codec) of a mobile terminal (shown by the curve600 in FIG. 6), starts to attenuate below the resonance frequency,utilizing this effect to shape the curve. If a smoother curve isdesired, a finite impulse response (FIR) filter could be utilized, asshown by the curve 605 in FIG. 6, to provide fine tuning to thefrequency response of the micro-speaker assembly. Also note that, whileFIG. 6 does not illustrate the effective changes in the tuning volume ofthe second forward tuning volume 175, as shown in FIG. 4, the dependenceon such tuning volume of the first resonance is expected to be small.Thus, the first resonance could readily be moved to lower frequencies,for example, by increasing the volume of the first forward tuning volume160 to lower the first resonance frequency.

As illustrated by the discussion of the present invention above,micro-speakers in accordance with various embodiments of the presentinvention may support high alerting ring levels while maintainingadequate level frequency response for speaker phone mode in the voicefrequency range as well as extending frequency response bandwidth forpolyphonic melodies (MIDI, MP3, etc.). Such a frequency response may beprovided without requiring the use of a large opening size from thehousing of the micro-speaker assembly and, further, while allowing peakacoustic concerns in mobile terminal design to be addressed throughporting of the speaker to the top or side of the mobile terminal insteadof an earpiece. Furthermore, the porting of the micro-speaker may, invarious embodiments, be provided through the main antenna or otherfeatures of the mobile terminal such as a printed circuit board (PCB) ofthe mobile terminal.

As shown by the frequency response curves of FIGS. 4-6, in variousembodiments of the present invention, the micro-speaker 155 is tuned toprovide an amplitude response in the voice frequency range and a highamplitude response, greater than the response at the voice frequencyrange, at an alert frequency. The amplitude response in the voicefrequency range may be at least about −20 decibels (dB) or, in furtherembodiments, at least about −10 dB, when measured at about onecentimeter (cm). The alert frequency may be between about 3000 hertz andabout 4000 hertz as shown by the approximately 4000 hertz firstresonance for the alert frequency in FIG. 6. An amplitude response isalso provided, through the use of the double-resonator, in an extendedfrequency range above the voice frequency range, such as to at leastabout 8000 hertz or, as shown in FIG. 6, to at least about 10,000 hertz.The minimum amplitude response in the extended frequency range, as inthe voice frequency range, may be about −20 dB. The second resonancefrequency may be between about 6000 hertz and about 8000 hertz. Thus, invarious embodiments, the micro-speaker may be provided a bandwidth of atleast about 8000 hertz and, in further embodiments, a bandwidth of atleast about 10,000 hertz. Thus, the double-resonator provided by themicro-speaker assembly of the present invention may extend the frequencyresponse of the micro-speaker above the voice frequency range andprovide loud alert frequency signals.

FIG. 7 is a flowchart illustration of operations that may be carried outto tune a micro-speaker 155 according to various embodiments of thepresent invention. As illustrated in the flowchart of FIG. 7, operationsfor tuning of the micro-speaker 155 include selecting a volume of firstforward tuning volume adjacent a front face of the micro-speaker todefine a first resonance frequency of a micro-speaker. (Block 200). Thefirst resonance frequency provides at least a minimum amplitude ofresponse in the voice frequency range (about 300 hertz to about 3400hertz). It further provides a high amplitude response, greater than theresponse of the voice frequency range, at the first resonance frequencywhich may, therefore, be used as an alert frequency. The volume of asecond forward tuning volume and the position of the second forwardtuning volume on a passageway of the micro-speaker assembly extendingfrom the first forward tuning volume to the opening in a housingcontaining the micro-speaker assembly is selected. (Block 205). Theselection of the volume and position of the second forward tuning volumemay be used to define a second resonance frequency of the micro-speaker.The second resonance frequency is greater (at a higher frequency) thanthe first resonance frequency. In some embodiments of the presentinvention tuning operations include selecting a volume for a back tuningvolume (Block 210).

The flowcharts, flow diagrams and block diagrams of FIGS. 1 and 7illustrate the architecture, functionality, and operation of possibleimplementations of methods for tuning micro-speaker assemblies. In thisregard, each block in the flow charts or block diagrams may represent amodule, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logical act(s).It should also be noted that, in some alternative implementations, theacts noted in the blocks may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may be executed inthe reverse order, depending upon the functionality involved.

In the drawings and specification, there have been disclosed typicalillustrative embodiments of the invention and, although specific termsare employed, they are used in a generic and descriptive sense only andnot for purposes of limitation, the scope of the invention being setforth in the following claims.

1. A mobile terminal, comprising: a portable housing; a micro-speakerpositioned in the housing, the micro-speaker comprising a housingincluding a vibratory member mounted therein and defining a plane of themicro-speaker; a first forward tuning volume adjacent a front face ofthe micro-speaker; a passageway extending from the first forward tuningvolume to an opening in the housing; and a second forward tuning volumein fluid communication with the passageway and positioned at a locationbetween the first forward tuning volume and the opening in the housing,the second forward tuning volume, the first forward tuning volume andthe passageway defining a double-resonator that tunes a frequencyresponse of the micro-speaker; wherein the first forward tuning volumeincludes the entire area in front of and adjacent the micro-speaker andextends in a plane substantially parallel to the plane of themicro-speaker and the passageway is an extension of the first forwardtuning volume extended to an outside opening in the phone housing, atleast part of which passageway extends in the plane of the first forwardtuning volume and wherein the entire area of the first forward tuningvolume extending over the micro-speaker and the entire length of thepassageway are in the same plane.
 2. A mobile terminal, comprising: aportable housing; a micro-speaker positioned in the housing, themicro-speaker comprising a housing including a vibratory member mountedtherein and defining a plane of the micro-speaker; a first forwardtuning volume adjacent a front face of the micro-speaker; a passagewayextending from the first forward tuning volume to an opening in thehousing; and a second forward tuning volume in fluid communication withthe passageway and positioned at a location between the first forwardtuning volume and the opening in the housing, the second forward tuningvolume, the first forward tuning volume and the passageway defining adouble-resonator that tunes a frequency response of the micro-speaker;wherein the first forward tuning volume includes the entire area infront of and adjacent the micro-speaker and extends in a planesubstantially parallel to the plane of the micro-speaker and thepassageway is an extension of the first forward tuning volume extendedto an outside opening in the phone housing, at least part of whichpassageway extends in the plane of the first forward tuning volume andwherein where the first forward tuning volume covers an area larger thana surface area of the micro-speaker.
 3. The mobile terminal of claim 2,wherein substantially all of the passageway extends in the plane of thefirst forward tuning volume.
 4. A mobile terminal, comprising: aportable housing; a micro-speaker positioned in the housing; a firstforward tuning volume in the housing external to the micro-speaker andadjacent a front face of the micro-speaker; a passageway extending fromthe first forward tuning volume to an opening in the housing, theopening having an area of less than about 10 square millimeters (mm²); asecond forward tuning volume in the housing in fluid communication withthe passageway and positioned at a location between the first forwardtuning volume and the opening in the housing, the second forward tuningvolume, the first forward tuning volume and the passageway defining adouble-resonator that tunes a frequency response of the micro-speaker,the frequency response defining an alert frequency between about 3000hertz (Hz) and about 4000 Hz and a minimum amplitude response in thevoice frequency range of at least about −10 decibels (dB) and anincreased frequency response having an amplitude response of at leastabout −20 dB in an extended frequency range up to at least about 8000hertz (Hz), the frequency response including a first resonant frequencyat about the alert frequency and a second resonant frequency betweenabout 6000 Hz and 8000 Hz; and a back tuning volume adjacent a side ofthe micro-speaker opposite the first forward tuning volume, wherein theback tuning volume is at least an order of magnitude larger than each ofthe first forward tuning volume and the second forward tuning volume.